A vacuum cleaner typically comprises a main body containing dirt and dust separating apparatus, a cleaner head connected to the main body and having a suction opening, and a motor-driven fan unit for drawing dirt-bearing air through the suction opening and the cleaner head, and into the main body. The suction opening is directed downwardly to face the floor surface to be cleaned. The dirt-bearing air is conveyed to the separating apparatus so that dirt and dust can be separated from the air before the air is expelled to the atmosphere. The separating apparatus can take the form of a filter, a filter bag or, as is known, a cyclonic arrangement.
Vacuum cleaners generally include cylinder, or canister, cleaners, upright cleaners and hand-held cleaners. A cylinder vacuum cleaner includes a main body supported by a set of wheels which is dragged along a floor surface by a hose and wand assembly extending between the main body and the cleaner head. The cleaner head is generally releasably attached to the end of the wand which is remote from the main body. An upright vacuum cleaner typically comprises a main body, a rolling assembly mounted on the main body for maneuvering the vacuum cleaner over a floor surface to be cleaned, and a cleaner head mounted on the main body. In use, a user reclines the main body of the upright vacuum cleaner towards the floor surface, and then sequentially pushes and pulls a handle which is attached to the main body to maneuver the vacuum cleaner over the floor surface.
A driven agitator, usually in the form of a brush bar, may be rotatably mounted within a brush bar chamber of the cleaner head. The brush bar comprises an elongate cylindrical core bearing bristles which extend radially outward from the core. The bristles are generally provided in clumps or tufts of bristles spaced about and along the core of the brush bar. The suction opening is located at the bottom of the brush bar chamber, and the brush bar is mounted within the chamber so as to protrude by a small extent through the suction opening. An exhaust port of the brush bar chamber is generally located towards the rear of the brush bar chamber. The exhaust port is usually in the form of a circular or rectangular aperture formed in the brush bar chamber.
The brush bar is activated mainly when the vacuum cleaner is used to clean carpeted surfaces. Rotation of the brush bar about its longitudinal axis may be driven by an electric motor powered by a power supply derived from the main body of the cleaner, or by a turbine driven by an air flow passing through or into the cleaner head. For example, WO2004/028330 describes a cleaner head having a turbine assembly for driving the rotation of a brush bar of the cleaner head. The turbine assembly comprises a vaned impeller which is mounted within a housing for rotation relative to a guide vane plate. The housing is located on one side of the floor tool. The impeller is connected to the brush bar by a pulley system. The housing has an air outlet connected to a suction duct extending between the suction opening and the main body of the vacuum cleaning appliance, and an air inlet for admitting ambient air into the housing. When the appliance is switched on, ambient air is drawn through the housing, causing the impeller to rotate and drive the rotation of the brush bar.
The rotation of the brush bar causes the bristles to be swept between the fibers of the carpet to be cleaned, agitating both the fibers of the carpet and any debris, such as dust particles, fibers and hairs, located on the surface of the carpet and/or between the fibers of the carpet. As the bristles are swept between the fibers, the force applied to the bristles by the carpet causes the bristles to splay, resulting in some debris becoming lodged between the bristles. As the bristles are rotated away from the fibers, the motion of the bristles as they return to their normal configuration tends to cause dust particles or other relatively small items of debris to be dislodged from the tufts of bristles. However, debris such as fibers and hairs can remain trapped between the bristles. With the rotation of the brush bar about its longitudinal axis, any such trapped fibers tend to move inwardly towards the core of the brush bar, resulting in the fibers becoming wrapped around the core of the brush bar. The user is then required to remove these hairs and fibers manually from the brush bar from time to time.
During a cleaning operation, a relatively high torque may be applied to the bristles of the brush bar, especially during the cleaning of a rug or a deeply piled carpet. To restrict the magnitude of the torque applied to the brush bar, and thereby reduce the risk of the brush bar stalling during a cleaning operation, the brush bar may be provided with relatively soft bristles, and/or a relatively low density of bristle tufts over the outer surface of the core of the brush bar. While reducing the risk of the brush bar stalling during the cleaning of deeply piled carpets, the provision of soft bristles and/or a low number of bristles tufts can impair the cleaning performance of the cleaner head when used on short piled carpets.